Allow null values to be cached with @CacheResult

Even though the JSR-107 spec forbids to store null values, our cache
abstraction allows that behaviour with a special handled (and this is
the default behaviour).

While this was working fine with our own set of annotations, the
JSR-107 interceptor counterpart was interpreting the spec sensu strictu.

We now allow for that special case as well.

Issue: SPR-13641

Author: snicoll

spring-aspects/src/test/java/org/springframework/cache/config/AnnotatedClassCacheableService.java

@@ -38,6 +38,11 @@ public Object cache(Object arg1) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	public Object cacheNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	public Object conditional(int field) {
 		return null;

spring-aspects/src/test/java/org/springframework/cache/config/AnnotatedJCacheableService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -58,6 +58,12 @@ public Long cache(String id) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@CacheResult
+	public Long cacheNull(String id) {
+		return null;
+	}
+
 	@Override
 	@CacheResult(exceptionCacheName = "exception", nonCachedExceptions = NullPointerException.class)
 	public Long cacheWithException(@CacheKey String id, boolean matchFilter) {

spring-aspects/src/test/java/org/springframework/cache/config/CacheableService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,6 +26,8 @@ public interface CacheableService<T> {
 
 	T cache(Object arg1);
 
+	T cacheNull(Object arg1);
+
 	void invalidate(Object arg1);
 
 	void evictEarly(Object arg1);

spring-aspects/src/test/java/org/springframework/cache/config/DefaultCacheableService.java

@@ -40,6 +40,12 @@ public Long cache(Object arg1) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable("testCache")
+	public Long cacheNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	@CacheEvict("testCache")
 	public void invalidate(Object arg1) {

spring-context-support/src/main/java/org/springframework/cache/jcache/interceptor/CacheResultInterceptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -59,9 +59,7 @@ protected Object invoke(CacheOperationInvocationContext<CacheResultOperation> co
 
 		try {
 			Object invocationResult = invoker.invoke();
-			if (invocationResult != null) {
-				cache.put(cacheKey, invocationResult);
-			}
+			cache.put(cacheKey, invocationResult);
 			return invocationResult;
 		}
 		catch (CacheOperationInvoker.ThrowableWrapper ex) {

spring-context-support/src/test/java/org/springframework/cache/jcache/config/AbstractJCacheAnnotationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -67,6 +67,23 @@ public void cache() {
 		assertSame(first, second);
 	}
 
+	@Test
+	public void cacheNull() {
+		Cache cache = getCache(DEFAULT_CACHE);
+
+		String keyItem = name.getMethodName();
+		assertNull(cache.get(keyItem));
+
+		Object first = service.cacheNull(keyItem);
+		Object second = service.cacheNull(keyItem);
+		assertSame(first, second);
+
+		Cache.ValueWrapper wrapper = cache.get(keyItem);
+		assertNotNull(wrapper);
+		assertSame(first, wrapper.get());
+		assertNull("Cached value should be null", wrapper.get());
+	}
+
 	@Test
 	public void cacheException() {
 		String keyItem = name.getMethodName();

spring-context-support/src/test/java/org/springframework/cache/jcache/config/JCacheableService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,8 @@ public interface JCacheableService<T> {
 
 	T cache(String id);
 
+	T cacheNull(String id);
+
 	T cacheWithException(String id, boolean matchFilter);
 
 	T cacheWithCheckedException(String id, boolean matchFilter) throws IOException;

spring-context-support/src/test/java/org/springframework/cache/jcache/interceptor/AnnotatedJCacheableService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -57,6 +57,12 @@ public Long cache(String id) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@CacheResult
+	public Long cacheNull(String id) {
+		return null;
+	}
+
 	@Override
 	@CacheResult(exceptionCacheName = "exception", nonCachedExceptions = NullPointerException.class)
 	public Long cacheWithException(@CacheKey String id, boolean matchFilter) {

spring-context/src/test/java/org/springframework/cache/config/AbstractAnnotationTests.java

@@ -89,6 +89,21 @@ public void testCacheable(CacheableService<?> service) throws Exception {
 		assertSame(r1, r3);
 	}
 
+	public void testCacheableNull(CacheableService<?> service) throws Exception {
+		Object o1 = new Object();
+		assertNull(cm.getCache("testCache").get(o1));
+
+		Object r1 = service.cacheNull(o1);
+		Object r2 = service.cacheNull(o1);
+		Object r3 = service.cacheNull(o1);
+
+		assertSame(r1, r2);
+		assertSame(r1, r3);
+
+		assertEquals(r3, cm.getCache("testCache").get(o1).get());
+		assertNull("Cached value should be null", r3);
+	}
+
 	public void testEvict(CacheableService<?> service) throws Exception {
 		Object o1 = new Object();
 
@@ -457,6 +472,11 @@ public void testCacheable() throws Exception {
 		testCacheable(cs);
 	}
 
+	@Test
+	public void testCacheableNull() throws Exception {
+		testCacheableNull(cs);
+	}
+
 	@Test
 	public void testInvalidate() throws Exception {
 		testEvict(cs);

spring-context/src/test/java/org/springframework/cache/config/AnnotatedClassCacheableService.java

@@ -40,6 +40,11 @@ public Object cache(Object arg1) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	public Object cacheNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	public Object conditional(int field) {
 		return null;

spring-context/src/test/java/org/springframework/cache/config/CacheableService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,8 @@ public interface CacheableService<T> {
 
 	T cache(Object arg1);
 
+	T cacheNull(Object arg1);
+
 	void invalidate(Object arg1);
 
 	void evictEarly(Object arg1);

spring-context/src/test/java/org/springframework/cache/config/DefaultCacheableService.java

@@ -41,6 +41,12 @@ public Long cache(Object arg1) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable("testCache")
+	public Long cacheNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	@CacheEvict("testCache")
 	public void invalidate(Object arg1) {

spring-context/src/test/resources/org/springframework/cache/config/cache-advice.xml

@@ -10,6 +10,7 @@
 	<cache:advice id="cacheAdviceInterface" cache-manager="cacheManager">
 		<cache:caching cache="testCache">
 			<cache:cacheable method="cache"/>
+			<cache:cacheable method="cacheNull"/>
 			<cache:cacheable method="conditional" condition="#classField == 3"/>
 			<cache:cacheable method="unless" unless="#result > 10"/>
 			<cache:cacheable method="key" key="#p0"/>